@Deacon.dog My understanding is that the dogs can interact casually, but they need to have well-established lives separate from each other, hence the separate walks, separate training sessions, separate sleeping areas, etc. When puppies become each other's whole world, it doesn't set them up for learning confidence or how to engage with others (dog or human) well, so establishing early on that the other puppy isn't any more important in their lives than, say, a neighbor's dog sets them up for a much healthier relationship with each other and the rest of the world.
Not sure there's a specific time at which you can say 'okay, we can stop everything' that will work for every household and every pair of puppies, but I'd imagine that if you're really on top of it things will slowly transition to a more 'normal' multi-dog household within the first year or so.
My late grandfather's dogs have this issue in spades. It's sad to see. The male constantly bullies the female, pushing between her and people or food or really anything she might find interesting, but they can't function without each other either. I worry for my grandmother when one of them passes, since she's stuck managing them largely on her own now that my grampa's gone.
